In a large bowl, beat egg with salt, Italian seasoning, red pepper flakes, and garlic. Add chopped onion, beef, turkey, bread crumbs, and Parmesan cheese; mix well. Shape mixture into 1-inch balls and brown in a large skillet. Drain meatballs and transfer to a 5-quart Crock-Pot.
In the same bowl, mix tomato sauce and wine; pour over meatballs. Cover and cook on Low for 5 1/2 to 6 hours.
To serve as sandwiches: Place 3 to 4 meatballs on 6-8 split rolls; top with sauce from Crock-Pot. If desired add shredded mozzarella cheese, red and yellow pepper strips, sliced onions, or olives.